Breathless from a six-mile bike ride to Madaket Beach, Ryan Dobbins smiles and says, "The world would be a better place if we all rode bikes." Here on Nantucket's southwestern shore, with Atlantic waves shimmering in the sunlight, it's easy to agree―especially when a seal pokes its head above the water to say hello. Now's the time to trade those car keys for a bike, a wicker basket, and the open road (or bike path).

At Young's Bicycle Shop, third-generation owner Harvey Young will set you up with the proper bike, helmet (yes, you must wear one), and map. Four distinct routes run east, west, and south, covering some 30 miles of paved paths. The longest, which parallels Polpis Road, is about 18 miles round trip. "You're going to find nature and scenery along the way," Harvey says. "Then you end up at the ocean, which is a wonderful place to break."

Thanks to Harvey's map, you won't get lost. From Nantucket Harbor, follow cobblestone streets lined with boutiques, museums, and restaurants to Polpis Road and the route toward Siasconset (or "'Sconset," as locals say). With the paved path under your wheels, you periodically view a kaleidoscope of color from towering trees and robust hedges. Migrant birds call above the crunch of scattered foliage. And as you pick up speed with every conquered hill and curve, you'll feel an adrenaline rush.

Along the way, you may catch glimpses of a windswept cranberry bog and Sesachacha Pond, where the trail leads to the red-and-white Sankaty Lighthouse. Built in 1850 and named for an Indian word that means "highland," the brick-and-stucco beacon still serves as a navigational aid. Although the Sankaty is not open to visitors, you may find the lighthouse moving: The 'Sconset Trust is relocating it some 400 feet northwest because of the eroding shoreline.

In Siasconset, you'll be treated to a vista of the historic community's traditional gray-shingle cottages running all the way to Ocean Avenue. There, the road curves and disappears into flawless blue sky, sapphire waves, and sandy shoreline. Like most off-season spots on Nantucket, it's nearly forsaken and may inspire you to set your kickstand, pull off your shoes and socks, and sprint toward the hypnotic scene. It's likely that this time of year only gulls will be watching. They may request a snack from your wicker bike basket, but hold tight to your carbohydrates―you'll need them for the final stretch.

To complete the popular Polpis route, you can return the way you came, or opt for the shorter Milestone Road. Though it's not as scenic, and the large hills can be intimidating to beginners, it's a faster way to town and the White Elephant hotel. There you can pamper your tired muscles in a guest room with nautical interiors, a cozy fireplace, and crisp organic linens. After pedaling all day, you might not want to travel far from your harbor- or garden-view suite for dinner. Luckily, the Brant Point Grill is attached to the White Elephant and offers awning-covered terrace dining. (Though Harvey may have cycling in his blood, he admits, "one of the main reasons people come to Nantucket is for the food.")

By morning, odds are you'll want to sample another Nantucket bike trail. "There are so many cool spots and unique places to discover," says Ryan Dobbins. "And every trail winds up at the beach."